The presence of significant quantities of H.sub.2 S and CO.sub.2 in various "sour" industrial gaseous streams poses a persistent problem. Although various procedures have been developed to remove and recover these contaminants, most such processes are deficient, for a variety of reasons.
In one cyclic method currently attracting attention, the sour gas is contacted, preferably with a solvent-reactant system which comprises a regenerable reactant, to provide solid free sulfur which is recovered either prior or subsequent to regeneration. Suitable reactant materials include polyvalent metallic ions, such as iron, vanadium, copper, manganese, and nickel, and include polyvalent metal chelates. Preferred reactants are coordination complexes in which the polyvalent metals form chelates with specified organic acids.
In yet another process, e.g., that disclosed in U.S. Pat. No. 4,091,073, issued May 23, 1978, to Winkler, CO.sub.2 present in the gaseous stream is also removed by the use of a suitable selective absorbent.
Other processes, such as that described in U.S. Pat. No. 3,226,320 to Meuly, involve removal of impurities from aqueous streams utilizing various polyvalent metal chelates.
Because these "cleanup" processes generally represent significant costs to manufacturing operations, any improvements in such processes which increase their efficiency may have great economic importance. For example, where ligands or chelates or polyvalent metals are employed, degradation or decomposition of the polyvalent metal chelates represents an important cost in the process, as well as requiring measures for decomposition product bleed or removal and addition of fresh solution. Even in the case of preferred chelates such as those of N-(2-hydroxyethyl) ethylene diamine triacetic acid and nitrilotriacetic acid, ligand decomposition, over a period of time, requires attention to prevent build-up of decomposition products and consequent loss of efficiency. As will be recognized, the bleed from such processes contains, along with the decomposition products, a considerable amount of the valuable chelate or chelates. A procedure for recovery of the chelate(s) or derivatives or precursors thereof could have great economic importance. The invention is such a process.